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# C1 help !!!!!!!!!! watch

1. Q. Find the set of values of x for which:

4x^2 - 3x - 1 < 0 and 4(x+20) < 15 - (x + 7)

Cant seem to factorise the quadratic
2. (Original post by Modesty)
Q. Find the set of values of x for which:

4x^2 - 3x - 1 < 0 and 4(x+20) < 15 - (x + 7)

Cant seem to factorise the quadratic
In usual fashion you want to find two numbers that add to make -3 and multiply to make -4.
3. (4X+1)(X-1)
4. (Original post by 13 1 20 8 42)
In usual fashion you want to find two numbers that add to make -3 and multiply to make -4.
Whoh.
The way i factorise is different i will put (4x ) (4x )
Find two numbers multiplyto give -3 add to give -1 i'm confused as to which two numbers??
5. (Original post by dons178)
(4X+1)(X-1)
I factorise differently , i put 4x in the beginning of both brackets but stuck
6. (Original post by Modesty)
Whoh.
The way i factorise is different i will put (4x ) (4x )
Find two numbers multiplyto give -3 add to give -1 i'm confused as to which two numbers??
You don't put 4x at the beginning of both. Think about what happens when you expand it; you'll get 16x^2.

You either do (4x )(x ) or (2x )(2x ).
7. (Original post by Modesty)
Whoh.
The way i factorise is different i will put (4x ) (4x )
Find two numbers multiplyto give -3 add to give -1 i'm confused as to which two numbers??
Well assuming you mean like (4x + ?)(4x + ?) that wouldn't work here..
multiply to make -4. You generally just want to exhaust the factors, positive and negative of the number AC in Ax^2 + Bx + C, until you find the two that also add to make B. Then you write out the x-term as the sum of two x terms whose coefficients are the two numbers and this allows you to factorize. Eventually you'll probably be able to factorize expressions like this very quickly just by experience/recognition
8. (Original post by ubisoft)
You don't put 4x at the beginning of both. Think about what happens when you expand it; you'll get 16x^2.
That's how i factorise quadratics when coefficient is greater than 1.
Why is it with this question i can't?
9. (Original post by Modesty)
That's how i factorise quadratics when coefficient is greater than 1.
Why is it with this question i can't?
Well it is wrong, don't do that. Expand it out and you will see it's not the same.
10. (Original post by 13 1 20 8 42)
Well assuming you mean like (4x + ?)(4x + ?) that wouldn't work here..
multiply to make -4. You generally just want to exhaust the factors, positive and negative of the number AC in Ax^2 + Bx + C, until you find the two that also add to make B. Then you write out the x-term as the sum of two x terms whose coefficients are the two numbers and this allows you to factorize. Eventually you'll probably be able to factorize expressions like this very quickly just by experience/recognition
11. (Original post by Modesty)
No. Note that 4x^2 - 3x - 1 = 4x^2 - 4x + x - 1. can you see how to factorize this?
12. (Original post by 13 1 20 8 42)
No. Note that 4x^2 - 3x - 1 = 4x^2 - 4x + x - 1. can you see how to factorize this?
Ahhhh i'm so stupid. I just remembered these are Trinomials.

Mutliply 4 * -1 = -4
Find two numbers which mutliply to give -4 and add to give 3
So (4x+4) (4x-1)

Now divide first bracket by 4 which gives x+1

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